Residual conductivity and electron phonon interaction in CdS

In the present paper we report an investigation concerning the electron-phonon interaction in a piezoelectric semiconductor during the phase of residual conductivity. Both from experimental data and from, a semi-quantitative theoretical approach we show that an intimate connection exists between the two phenomena. In particular, during the phase of normal conductivity (sample under illumination) the dominant mechanism of the electron-phonon interaction is classical in character, while during the phase of residual conductivity the dominant mechanism is a quantistic one, irrespectively of the value of the conductivity. In addition we show that the details of the decay in time of the current during the phase of residual conductivity can be explained only by taking into account the electron-phonon interaction processes, the behaviour of the sample being Ohmic only at the critical voltage.